hoalapthe vn
TRANSCRIPT
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HHA LA LP THP TH
StereochemistryStereochemistry
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Chirality Handedness: gng tay phi khng
chng kht vi gng tay tri. i tng nh qua gng khc vi itng gc ban u.
=>
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Chiral Carbons Carbon t din vi 4 nhm th khc
nhau l chiral. nh qua gng ca n s l hp cht
khc nhau (enantiomer). =>
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Mt phng i xng gng
Nu hai nhm gingnhau, carbon lachiral.
Phn t c mt phngi xng th khng lchiral.*
Lu ! Nu khng c mt phng i xng,phn tc th l chiral hoc achiral. nh quagng c chng kht ln nhau hay khng.
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H
Cl
H
Cl Are these twostructures identical?
mirror
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HCl
HCl
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enantiomersenantiomers
Cc ng phn lp
th
mnh quagng khng chng
kht ln nhau l
enantiomers.enantiomers.
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Stereoisomers ng phn hnh hc: cis-trans isomers.
Enantiomers: nonsuperimposable mirror images,different molecules.=>
cis-1,2-dichlorocyclopentane trans -1,2-dichlorocyclopentane
H
Cl
H
Cl
H
Cl
H
Cl
H
Cl
Cl
H
H
Cl
Cl
H
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diasteriomersdiasteriomers
CH3
CH3
H
H
cis
trans
ng phn lp th m
khng phi l nh quagng ca nhau ldiastereomers.diastereomers.
H
CH3
H
CH3
H
CH3
H
CH3
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Diastereomers
Stereoisomers that are not mirror images. Geometric isomers (cis-trans)
Cc phn t c hai hoc nhiu chiral carbons.
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Alkenes
Cis-trans isomers are not mirror images,so these are diastereomers.
C C
H H
CH3H3C
cis-2-butenetrans-2-butene
C C
H
H3C
CH3
H =>
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Properties of Diastereomers Diastereomers c tnh cht vt l khc
nhau: m.p., b.p. Tch d dng.
Enantiomers khc trong phn ng vicc phn t chiral khc v lm quaymt phng nh sng phn cc.
Enantiomers kh tch khi nhau.
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MMt phn tt phn t ll chiralchiralnnu 2u 2 nh qua gng cnh qua gng caa
chchng khng chng khng chng khng kht ln nhau.t ln nhau.
A molecule isA molecule is achiralachiralif its two mirror image formsif its two mirror image forms
areare chchng khng kht (superposable).t (superposable).
ChiralityChirality
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BrBrClCl
HH
FF
Bromochlorofluoromethane is chiralBromochlorofluoromethane is chiral
It cannot beIt cannot besuperposed pointsuperposed point
for point on itsfor point on itsmirror image.mirror image.
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BrBrClCl
HH
FF
Bromochlorofluoromethane is chiralBromochlorofluoromethane is chiral
HH
ClClBrBr
FF
cho thcho thy khng chy khng chngngkhkht, quay phn tt, quay phn t 180180quanh trquanh trc c ng.ng.
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BrBrClCl
HH
FF
Bromochlorofluoromethane is chiralBromochlorofluoromethane is chiral
HH
ClClBrBr
FF
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Another lookAnother look
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are enantiomers with respect to each otherare enantiomers with respect to each other
vv
nh qua gng khng chnh qua gng khng chng khng khttll enantiomersenantiomers
EnantiomersEnantiomers
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IsomersIsomers
ConstitutionalConstitutionalIsomersIsomers
StereoisomersStereoisomers
EnantiomersEnantiomers DiastereomersDiastereomers
Stereoisomersthat are not
mirror images.
Stereoisomers thatare nonidentical
mirror images
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ChlorodifluoromethaneChlorodifluoromethaneis achiralis achiral
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ChlorodifluoromethaneChlorodifluoromethaneis achiralis achiral
hai chai cu tru trc lc lnh qua gngnh qua gng,,nhng khng lnhng khng lenantiomers,enantiomers,bbi vi v chchngng
chchng khng khttc ln nhau.c ln nhau.
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Trung tm lTrung tm lp thp th
The Stereogenic CenterThe Stereogenic Center
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Nguyn tNguyn t carboncarboncc bbn nhn nhm thm th khkhc nhauc nhau
ccng ng c gc gi:i:chiral centerchiral centerasymmetric centerasymmetric centerstereocenterstereocenter
The Stereogenic CenterThe Stereogenic Center
ww
xx yy
zz
CC
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A molecule with a single stereogenicA molecule with a single stereogenic
center is chiral.center is chiral.
BromoBromochlorochlorofluorofluoromethanemethane is an example.is an example.
Chirality and stereogenic centersChirality and stereogenic centers
ClCl FF
BrBr
HH
CC
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A molecule with a single stereogenicA molecule with a single stereogenic
center is chiral.center is chiral.
22--Butanol is another example.Butanol is another example.
Chirality and stereogenic centersChirality and stereogenic centers
CHCH33
OHOH
HH
CC CHCH22CHCH33
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Examples of molecules with 1 stereogenic centerExamples of molecules with 1 stereogenic center
CHCH33
CC
CHCH22CHCH33
CHCH22CHCH22CHCH22CHCH33CHCH33CHCH22CHCH22
a chiral alkanea chiral alkane
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Examples of molecules with 1 stereogenic centerExamples of molecules with 1 stereogenic center
Linalool, a naturally occurring chiral alcoholLinalool, a naturally occurring chiral alcohol
OHOH
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Examples of molecules with 1 stereogenic centerExamples of molecules with 1 stereogenic center
1,21,2--Epoxypropane: a stereogenic centerEpoxypropane: a stereogenic center
can be part of a ringcan be part of a ring
OO
HH22CC CHCHCHCH33
attached to the stereogenic center are:attached to the stereogenic center are:
HH
CHCH33OCHOCH22
CHCH22OO
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Examples of molecules with 1 stereogenic centerExamples of molecules with 1 stereogenic center
Limonene: a stereogenicLimonene: a stereogenic
center can be part of acenter can be part of aringring
CHCH33
HH CC
CHCH33
CHCH22
attached to theattached to thestereogenic center are:stereogenic center are:
HH
CHCH22CHCH22CHCH22CH=CH=
C=C=
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MMt phn tt phn t chchcc 1 stereogenic center1 stereogenic center
phphi li l chiral.chiral.
nhngnhng, m, mt phn tt phn t cc 2 ho2 hoc nhic nhiuu
stereogenic centers cstereogenic centers c thth ll chiralchiralhohoc khngc khng
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i xi xng trong nhng trong nhng cng cu tru trc achiralc achiral
Symmetry in AchiralSymmetry in AchiralStructuresStructures
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Symmetry tests forSymmetry tests forachiralachiral structuresstructures
Phn tPhn t cc mmt pht phng ng i xi xng hong hoc trung tm c trung tm i xi xngngll achiralachiral..
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A plane of symmetry bisects a molecule into twoA plane of symmetry bisects a molecule into twomirror image halves. Chlorodifluoromethanemirror image halves. Chlorodifluoromethane
has a plane of symmetry.has a plane of symmetry.
Plane of symmetryPlane of symmetry
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A plane of symmetry bisects a molecule into twoA plane of symmetry bisects a molecule into twomirror image halves. Chlorodifluoromethanemirror image halves. Chlorodifluoromethane
has a plane of symmetry.has a plane of symmetry.
Plane of symmetryPlane of symmetry
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A molecule with a plane of symmetrycannot be chiral Example
2-Chloropropane (a) has a plane of symmetry but 2-chlorobutane (b) does not
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A plane of symmetry bisects a molecule into twoA plane of symmetry bisects a molecule into twomirror image halves.mirror image halves.11--BromoBromo--11--chlorochloro--22--fluoroethene has a planefluoroethene has a plane
of symmetry.of symmetry.
Plane of symmetryPlane of symmetry
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A plane of symmetry bisects a molecule into twoA plane of symmetry bisects a molecule into twomirror image halves.mirror image halves.11--BromoBromo--11--chlorochloro--22--fluoroethene has a planefluoroethene has a plane
of symmetry.of symmetry.
Plane of symmetryPlane of symmetry
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A point in the center of theA point in the center of themolecule is a center ofmolecule is a center ofsymmetry if a line drawnsymmetry if a line drawnfrom it to some element,from it to some element,when extended an equalwhen extended an equal
distance in the oppositedistance in the oppositedirection, encounters andirection, encounters an
identical element.identical element.
Center of symmetryCenter of symmetry
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Locating a Stereocenter (ChiralCarbon)
CH3 CH C
OH
OH
O
Lactic acid
*
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CH3 CH2 CH2 CH2 CH2 C CH2 CH2 CH2 CH3
Br
H
*
Locating a Stereocenter
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Locating a Stereocenter
O
CH3
H*
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Locating a Stereocenter
H CH3no stereocenter
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Carvone: mirror-image isomershave different flavors and odors!
O
CH3
C
CH3
CH2
*
Enantiomers. Many of the properties of
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y p penantiomers are identical.
ClH
HClsolubility in water
boiling point
melting point
Enantiomers. However, if enantiomers are
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,different compounds they must have adifferent names and different properties.
ClH
HClRotation of the plane ofpolarized light (opticalrotation).
Taste and smell
biological activity(R)-2-chlorobutane
(S)-2-chlorobutane
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Enantiomers have differentb iolog ical act iv i ty .
Enantiomers have different properties
H
O
H
O
(-)-carvone
oil of spearmint(+)-carvone
oil of caraway
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H
O
H
O
(-)-carvone
oil of spearmint(+)-carvone
oil of caraway
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The Biological Importance of Chirality The binding specificity of a chiral receptor sitefor a chiral molecule is usually only favorable inone way
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"How would you like tolive in Looking-GlassHouse, Kitty? I wonder ifthey'd give you milk inthere? Perhaps Looking-glass milk isn't good to
drink...".
Through the Looking Glass by
Lewis Carroll
Alice looked through the keyhole of this door into the Looking Glass garden (the Cathedral garden)
Is looking glass
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Is looking glass
milk safe to drink?
?
Different enantiomers of a drug
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ff m f g
can have different effects.
amphetamineH2NNH2H H
stimulant adversecardiovasculareffects
Problem: Are A and B identical or enantiomers?
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Problem: Are A and B identical or enantiomers?
Manipulate B to see if it will become superposable with A
Exchange 2 groups to try to convert B into A One exchange of groups leads to the enantiomer of B
Two exchanges of groups leads back to B
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The Cahn Ingold PrelogThe Cahn Ingold Prelog
RR--SS Notational SystemNotational System
Assign (R) or (S)
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g ( ) ( )
Assign a priority number to each group attached tothe chiral carbon.
Atom with highest atomic number assigned the
highest priority #1 Working in 3D, rotate molecule so that lowestpriority group is in back.
Draw an arrow from highest to lowest priority group. Clockwise = (R), Counterclockwise = (S)
If the order of decreasing precedence traces aIf the order of decreasing precedence traces aclockwise path the absolute configuration isclockwise path the absolute configuration is RR If theIf the
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ab
c
d
a b
c
d
Order of decreasing rank:Order of decreasing rank:
aa >> bb > c >> c > ddclockwiseclockwise
RRanticlockwiseanticlockwise
SS
clockwise path, the absolute configuration isclockwise path, the absolute configuration is RR. If the. If the
path is anticlockwise, the configuration ispath is anticlockwise, the configuration is SS..
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((SS))--22--ButanolButanol
CC OHOH
HH33CC
HHCHCH33CHCH22
Enantiomers of 2Enantiomers of 2--butanolbutanol
CCHOHO
CHCH33
HH CHCH22CHCH33
((RR))--22--ButanolButanol
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The CahnThe Cahn--IngoldIngold--Prelog RulesPrelog Rules
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Orient the molecule so that lowest-ranked (lightest)substituent points away from you. Trace the path fromhighest to lowest. Clockwise (R), Counter Clockwise (S)
E ti f 2E ti f 2 b t lb t l
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((SS))--22--ButanolButanol
CC OHOH
HH33CC
HHCHCH33CHCH22
Enantiomers of 2Enantiomers of 2--butanolbutanol
CCHOHO
CHCH33
HH CHCH22CHCH33
((RR))--22--ButanolButanol
St i t i iSt i t i i
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HHHH33CC
HH
HH
Stereogenic center in a ringStereogenic center in a ring
R or S ?R or S ?
RR
CHCH22C=C >C=C > CHCH22CHCH22 >> CHCH33 >> HH
Groups with double or triple bonds are assignedi iti if th i t d li t d
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priorities as if their atoms were duplicated ortriplicated
Vinyl vs isopropylVinyl vs isopropyl
Problem: Are A and B identical or enantiomers?
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Name them using R- S- designation
(R)(R)
--11
--bromobromo
--1chloroethane1chloroethane
http://www.cem.msu.edu/~reusch/VirtualText/sterism3.hthttp://www.cem.msu.edu/~reusch/VirtualText/sterism3.ht